When the number of pixels in an output image is greater than the number of pixels in the input image, an image processing apparatus must generally carry out an image enlargement process. In conventional image processing apparatus, the image is enlarged by taking weighted sums of the pixel values of pixels neighboring the pixel of interest.
The image processing apparatus described in Patent Document 1, for example, has a computational circuit for multiplying the data of five pixels mutually adjacent in the main scanning direction, which are output from shift registers, by predetermined weighting constants, and adding the resulting products obtained from the pixel data; in image data enlargement processing, the result of this computation in the computational circuit is selected by a selector as the pixel data at the center of these pixel data.    Patent Document 1: Japanese Patent Application Publication No. H6-311346 (FIG. 1)